A. Field of the Invention
The invention generally concerns the treatment of gaseous streams to remove C3+ hydrocarbons. In particular, the invention relates to contacting a gaseous stream with organosilica particles to remove C3+ hydrocarbons and the regeneration of the organosilica particles.
B. Description of Related Art
Natural gas produced from oil and gas wells normally includes a mixture of hydrocarbon components having varying boiling points. That is, a gas stream produced from a well contains a mixture of hydrocarbon components which exist in the vapor phase at the particular pressure and temperature levels at which the well is produced. If the gas stream pressure is changed or the temperature is decreased, or both, some of the hydrocarbon components contained in the gas stream are liquefied or condensed. The temperature at which some of the components of a gas stream comprised of hydrocarbons will condense at a particular pressure level is known as the hydrocarbon dew point (HCDP) of the gas stream.
Transporting gas streams with a high HCDP from remote natural gas wells can create a risk of condensate formation in the pipelines. As the gas passes through the transmission pipeline, the pressure of the gas drops due to friction, and particularly during the winter months, the temperature of the gas is lowered due to atmospheric conditions. Thus, condensable components contained within the gas stream passing through the pipeline are condensed. Additionally, if the gas contains large quantities of heavy hydrocarbons, then the HCDP of the gas will be high and small changes in the temperature or the pressure of the gas are more likely to cause liquids to condense out of the gas. Formation of condensate is detrimental in that the flow of gas through the system is impaired and can cause severe problems for downstream equipment, or may result in explosions or fires.
Various methods and apparatuses have been developed for removing condensable components from gas streams prior to the gas entering the transmission pipe line. Most liquid hydrocarbon droplets entrained in the gas stream can be removed using conventional separation technologies. One of the first steps in processing gas involves putting it though a 2-phase or 3-phase separator, which allows liquid hydrocarbons to fall out of the gas by gravity separation. Additional separation is often achieved with a coalescing filter which uses physical barriers to impede the flow of liquid droplets while allowing the vapor to pass through. Although these technologies are efficient at bulk removal of liquid droplets, they suffer from the inability to remove extremely small droplets let alone heavy hydrocarbons that are still in the vapor phase; thus, they cannot significantly reduce the HCDP of the stream.
Technologies for reduction of HCDP may require manipulation of the thermodynamic properties of the gas stream. In mechanical refrigeration, the stream is cooled to a temperature at which all of the heavy hydrocarbons condense out of the vapor phase and can be removed from the stream in a controlled manner. Joule-Thomson (J-T) throttling involves rapid depressurization of the gas stream which cools the gas and forces the heavy hydrocarbons to condense. Although highly effective at reducing the HCDP of a natural gas stream, mechanical refrigeration and J-T throttling suffer from the requirement of a large energy input or an expenditure of the energy stored in the gas, respectively; thus these processes are not always economically viable to implement when limited utilities are available.
Some adsorbent media can also reduce the HCDP of natural gas streams by capturing the heaviest hydrocarbons in the vapor phase; silica (SiO2) gel, granular activated carbon (GAC), and some proprietary materials can be used in this way. These technologies suffer from large footprints depending on the volume of material needed, and they generate large quantities of waste if the material cannot be reused. The technologies also suffer in that they require medium to high pressures to lower the hydrocarbon dew point value of the natural gas stream.